With rising and development of flat display devices, low temperature polysilicon technique has become a synonym for high quality display devices. In recent years, major manufacturers of display panel begin to invest and build low-temperature polysilicon (LTPS) production lines in sequence due to its rapid development and promising future.
Excimer laser annealing process is an important step for forming polysilicon. In a conventional excimer laser annealing (ELA) apparatus, it is required to place a substrate onto a substrate stage manually. However, it is difficult to distinguish between the glass side of the substrate and a silicon side of the substrate on which an a-silicon film is formed because the two sides are similar in color. Mistakes are prone to occur in visually discriminating the two sides from each other. If a mistake occurs, serious consequences will be caused. For example, if the glass side of the substrate is placed upward by mistake and is irradiated by a laser beam, the laser beam will pass through the substrate and is irradiated on an alignment film (e.g., PI film), and this irradiation may cause the alignment film to be ashed and the ash thus produced is diffused around the process chamber of an LEA apparatus, which causes the apparatus contaminated and unnecessary cost to clean the process chamber.